The prediabetic/diabetic condition functionally alters the microvascular bed of the eye, kidney and heart. In diabetic retinopathy, retinal microvessels have increase permeability, exhibit thickened basement membranes and frequently lose pericytes. The relationship between changes in these barrier components and changes in permeability remains unclear. Increased retinal microvessel permeability often precedes detectable alterations in microvessel structure and vision impairment and may be one of the central physiological defects in diabetic retinopathy. Current theories of vascular leak account for an increase in flux either by an increase intravascular pressure of surface area, or by direct changes in the permeability of the endothelial barrier. In an vitro systems, we have shown previously that, without changes in pressure or surface area, endothelial monolayers later their permeability characteristic in response to autocoids and hormones. The objective of this proposal is to develop an in vitro models system useful for determining how retinal microvessel barrier is maintained and how this barrier is compromised in diabetic retinopathy. We first proposed to develop a model of the retinal vasculature consisting of retinal capillary endothelial cells cultured on porous microcarriers beads and perfused in chromatographic cell-columns. This model design permits sensitive detection of changes in retinal endothelial permeability. Secondly, we propose to compare the properties of this barrier to endothelia barrier formed by endothelia cells from other organs. And thirdly, we will examine the effects of three unique retinal/diabetic environmental factors that may influence this barrier's significantly from previous investigations of the increased permeability associated with diabetic retinopathy, and in our preliminary results we describe, to our knowledge, the first measurements of the permeability of the retinal capillary endothelial barrier in vitro. Identification of the specific mediators and mechanisms which lead to the loss of retinal microvascular barrier in diabetes may help to improve the management of ocular complications stemming from diabetes.